Magneto-resistive random access memory (MRAM) is non-volatile random access memory technology that has been under development sine 1995 by Motorola (the division later became Freescale); in 2000, Spintec laboratory filed first Spin Torque Transfer (STT) patent, which utilizes a spin-polarized current through the tunneling magneto-resistance layer to write data, and consumes less power and is more scalable than conventional MRAM; in 2005, Renesas Technology and Grandis collaborated on development of 65 nm MRAM employing STT, and Sony announced the first lab-produced spin-torque-transfer MRAM, with further advances in materials, this process should allow densities higher than those possible in DRAM. However, now it has manufacturability problem, and so it is still far away from volume production and is extreme expensive (in term of $ per Gb) due to three main backwards: (1) large bias point variation, (2) reading performance variation - - - large amplitude (AMP) and asymmetry (ASYM) range variation, (3) writing performance variation - - - poor write-ability, means switching between states sometimes cannot be completed in given time, and (4) outlier cells (in bias and performance) are the main limitation for MRAM, even though it is not a limitation recording head of hard disk drive. Due to these backwards (1) and (2), it is difficulty to use coding, decoding and equalization methods which are currently used in hard disk drive.
patent/application No.timeinventors7,309,617December 2007Ruehrig et al.7,345,912March 2008Luo et al.7,453,747November 2008Abraham el al7,747,926June 2010Wise et al.7,933,137April 2011Dimitrov, et al.8,248,841August 2012Yang8,281,221October 2012Sakimura, et al.8,320,167November 2012Rao, et al.8,462,543Jun. 11, 2013Zheng; Yuankai et al2010/0177558July 2010Sakimura et al.